The present invention relates broadly to an electromagnetic interference (EMI) shielded or grounded panel assembly including a porous, electrically-conductive shielding media and an electrically-conductive frame for supporting the media, and more particularly to such an assembly which is adapted to cover a corresponding ventilation opening in an electronics housing or other enclosure enclosures and which accommodates the flow of cooling air into the enclosure while maintaining electrical continuity and EMI shielding effectiveness across the opening.
The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed xe2x80x9celectromagnetic interferencexe2x80x9d or xe2x80x9cEMIxe2x80x9d as being known to interfere with the operation of other proximate electronic devices.
For attenuating EMI effects, shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other xe2x80x9ctargetxe2x80x9d devices from other source devices. Such shielding is provided as a barrier which is interposed between the source and the other devices, and most often is configured as an electrically conductive and grounded housing or other enclosure, such as a room, which surrounds the EMI generating circuitry of the source device. However, when such circuitry is contained within the confined space of an enclosure, it often is necessary to provide a cooling or ventilation means to dissipate the heat which is ohmicly or otherwise generated by the circuitry. Most enclosures therefore are formed with one or more air intake and/or exhaust openings or ports for natural or forced convective circulation of air between the interior of the enclosure and the ambient environment.
Left uncovered, such openings would represent a discontinuity in the surface and ground conductivity of the enclosure, with the result of a decrease in the EMI shielding effectiveness of the enclosure. Accordingly, shielded vent panels have been proposed for covering the openings in an manner which allows for the ventilation of the enclosure while electrical continuity, i.e., grounding, across the vent opening is maintained. In basic construction, such vent panels, which are sized to span the corresponding opening in the enclosure, conventionally are formed as including a sheet of a porous, electrically-conductive shielding media, and an electrically-conductive frame member configured to support the media as extending about the outer periphery thereof. The media, which may be an expanded metal mesh or, alternatively, a honeycombed-structured or other cellular structured metal foil, is received in or otherwise is attached to the frame, which typically is provided as an extruded aluminum or other metal profile. The frame, in turn, may be fastened to the enclosure over the opening thereof with screws or the like, with a compressible, electrically-conductive seal or gasket optionally provided for improved electrical contact between the frame and the enclosure.
However, for electrical continuity to be maintained across the opening, good electrical contact must be provided not only as between the frame and the enclosure, but also as between the media and the frame. In this regard, conventional panels may employ a C-shaped frame channel including a V-shaped or other projection integrally formed within one of the sides of the channel. With the peripheral edges of the media being received within the channel, the sides thereof are compressed to cause the projection to penetrate into the media and thereby establish good electrical contact. Vent panels of such type are marketed commercially by the Chomerics Division of Parker-Hannifin Corp. (Woburn, Mass. under the tradenames xe2x80x9cCho-Cell(trademark),xe2x80x9d xe2x80x9cShield Cell(copyright),xe2x80x9d and xe2x80x9cOmni Cell(copyright).xe2x80x9d Alternatively, the media may be fit into the frame and then bonded thereto using a conventional joining technique such as resistance welding, brazing, soldering, or the like.
Another method of attaching the media to the frame involves using the gasket typically provided between the frame and the enclosure to hold the filter media in place. As is described in commonly-assigned U.S. Pat. No. 5,032,689, the frame in such method may be integrally-formed as including a ridge over which the gasket is press-fitted for its retention about the periphery of the frame. The gasket, in turn, may be configured to overlap the media for securing the media to the frame.
U.S. Pat. No. 3,580,981 discloses another shielding vent panel wherein an electrically conductive textile is positioned about the periphery of the media for contact between the media and the frame which may have an L-shaped or generally Z-shaped profile. To assure good conductivity, the frame, media, and textile are covered with an electrically-conductive coating or plating such as by immersion in a molten tin or metal bath. Other vents and materials therefor are described in U.S. Pat. Nos. 3,546,359; 3,553,343; 3,584,134; 3,821,463; and 4,616,101.
In view of the continued proliferation of electronic devices, it is to be expected that continued improvements in EMI shielded vent panels would be well-received by industry, and particularly by semi-conductor manufacturers for use in the processing of silicon wafers and the like. A preferred seal construction would be economical to manufacture, but also would exhibit reliable shielding performance in assuring good electrical contact between the shielding media and the frame member.
The present invention is directed to an EMI shielded vent construction including an electrically-conductive frame member having a generally U- or C-shaped profile including and end wall portions and a pair of side wall portions integral with the end wall portion, and an electrically-conductive, porous shielding medium member, which is supported by the frame member. With the periphery of the shielding medium member being received within the frame member intermediate the lateral or side wall portions thereof, the frame member may be compressed, such as within a hydraulic platen press or the like, to retain the medium member therein. However, in accordance with the present invention, a resilient, electrically-conductive strip gasket element further is provided as interposed between the medium member and one of the side wall portions of the frame member prior to the compression thereof. Such gasket member conforms under the applied pressure to any irregularities between the interfacing surfaces of the medium member and the frame member in ensuring that a substantially continuous conductive pathway is developed across those surfaces without the provision of an additional conductive coating or plating. Advantageously, the provision of the gasket member obviates the need to integrally form a contact projection within the frame member, and thus allows the frame member to be constructed of a roll formed aluminum or other metal channel rather than of a more costly extruded profile. The use of roll formed channel, moreover, allows a continuous length thereof to be folded or otherwise shaped into a rectangular, square, or other closed geometry and thereby eliminates the need for welds at the frame member corners.
In one disclosed embodiment, the frame member is formed of aluminum or another metal, with the medium being formed of a layer of an aluminum or other metal foil which is folded, bent, or otherwise shaped into a cellular honeycomb structure to extend along a transverse axis intermediate a generally planar first and second face. Although the strip gasket element may be formed of any resilient, electrically conductive material such as a metal-filled elastomeric extrusion, or a foam extrusion sheathed in an electrically conductive mesh or fabric, an all-metal, knitted wire construction may be specified for economic or performance considerations. In a preferred construction, the compression of the frame member advantageously effects the compression of both the gasket and the peripheral edges of the medium to provide a greater surface area of electrical contact therebetween.
It is therefore a feature of the present invention to provide an electromagnetic interference (EMI) shielded vent panel construction for disposition over a corresponding opening formed within a surface of an electronics enclosure. The vent panel includes an electrically-conductive medium having an outer periphery and extending along a transverse axis intermediate a pair of faces defining a thickness dimension. Such dimension is supported within an electrically-conductive frame having a perimeter defining a closed geometric area selected to circumscribe the opening of the electronics enclosure. The frame is configured as having a generally C-shaped cross-sectional profile and includes an elongate end wall having an interior surface and an exterior surface, and a pair of oppositely-disposed side walls extending from the interior surface of the end wall. Each of the side walls has an outer surface, one of which is disposable about the opening of the enclosure in electrically-conductive adjacency with the surface thereof, and an inner surface spaced-apart a first predetermined distance from the inner surface of the other of the side walls. The outer periphery of the medium is received intermediate the inner surfaces of the side walls such that each of said walls extends over a corresponding edge portion of the faces of the medium. Along with the medium, an electrically-conductive gasket is disposed intermediate the inner surface of a first one of the side walls and the edge portion of a first one of the medium faces. The gasket extends along substantially the entire perimeter of the frame and is deflectable between the inner surface of said first one of said side walls and the edge portion of said first one of the faces of said medium. As assembled, the frame is compressed to space the inner surface of each of the side walls thereof a second predetermined distance from the inner surface of the other of said side walls deflecting the gasket into a collapsed orientation effective to provide substantially continuous electrical contact between the frame and the medium.
The present invention, accordingly, comprises the vent panel possessing the combination of elements and construction which are exemplified in the detailed disclosure to follow. Advantages of the present invention include a vent panel exhibits reliable EMI shielding and air flow characteristics. Additional advantages include a panel construction which is economical in allowing the use of a roll formed frame, and which ensures good electrical contact between the shielding medium and the frame without the need for a separate metal plating operation. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.